This invention relates to non-invasive methods for ablating eye tissue using an electric current delivered transclerally. A specific application of this invention includes reduction of intraocular pressure by focal destruction of the ciliary process.
Glaucoma is a potentially debilitating disease of the eye in which the intraocular pressure within the eye rises above normal levels. Glaucoma is generally treated by a surgical procedure where a small hole is introduced through the sclera, which is the outer coating of the eye, to allow fluid within the eye to drain into the subconjunctival space, between the conjunctiva and the sclera.
Cycloablation, which is a destruction of the ciliary body, is another method by which an ophthamologist can reduce intraocular pressure. The ciliary processes are involved in the production of fluid within the eye. Thus, by destroying the ciliary processes, aqueous production is reduced. Cycloablation is primarily prescribed for advanced glaucoma patients with poor vision.
At present there are a number of cycloablative or cyclodestructive procedures. These procedures include cyclocryotherapy, transscleral Nd:YAG laser cycloablation, therapeutic ultrasound, cyclodiathermy, and transpupillary argon ciliary process photoablation. There can be a significant post-treatment pressure spike, marked intraocular inflammation and unpredictability associated with each of these methods. The degree of unpredictability is such that in some cases phthisis bulbi ensues. A preferred technique would be one which is more predictable, and associated with minimal inflammation.
Iontophoresis, which is a means of introducing drugs in ionized form into tissues by means of electric current, has become increasingly popular in North America over the past several years. Its applications range from dye-enhanced ablation with laser sclerotomies to the experimental treatment of keratitis and endophthalmitis using antibiotics. Most research concerning the use of iontophoresis utilizes the method as a non-invasive mode of introducing effective levels of drugs to various regions of the eye, such as the vitreous humor. As a mode of drug administration, the prior art teaches regulation of current, probe diameter and time to avoid tissue damage. See, for example, U.S. Pat. No. 4,564,016 to Maurice et al.
One reference, Berens, Sheppard and Duel, Cvcloelectrolvsis for Glaucoma. J. Trans. Am. Opthamol. Soc. 47:364-382 (1949), describes the use of electricity to destroy the ciliary body. The technique described involves inserting a needle directly into the ciliary body. In a majority of cases, dissection of the conjunctiva was required and 50-75 punctures were recommended. While such invasive means alleviate ocular pressure, complications such as infections may arise which are related to the procedure.
Thus, there is a need for a non-invasive means for relieving intraocular pressure and an efficient, less traumatic means for ablating eye tissue.